(Note: the blue horizontal menu bar directly above lists the subsections of "Evolution According to Contemporary Science." Beginning with "How Has Life Evolved?," be sure to read each of these subsections before moving on to the next primary section, "Evil, Ethics, and Human Values in an Evolving World.")

The Evolutionary Roles of Pain, Suffering, and Death

Whereas many interpret Genesis 1-3 as attributing all physical suffering and death to the sin of Adam, the fossil record shows that living creatures not only died, but killed and ate each other, and even competed in evolutionary "arms races," for hundreds of millions of years before the first human sin. Such endless ages of "nature red in tooth and claw" scandalize many thinking people. Unlike most of the violence in our TV shows, however, these eons of bloodshed were not gratuitous, but absolutely unavoidable given the ground rules of Darwinian evolution. Nor are pain and death merely unfortunate by-products of the process: they play essential, constructive roles in the evolution of life.

Pain and suffering. Physical suffering results from the ability to feel pain. Pain is an alarm that warns animals away from the danger of injury, and conditions them to avoid similar dangers in the future. Unwelcome stimulation of sense organs through accident, disease, or environmental conditions causes discomfort (pain, heat, cold, fever, nausea, even anxiety) that may serve no apparent purpose; but this is deceiving. For example, we may vomit even when no really dangerous poison is in our stomachs, but this is erring on the safe side. Anxiety repels us from danger and drives us to seek companionship and security in numbers. This could have stimulated the evolution of our strong social bonds—an unexpected dividend from an emotion we tend to list among life's liabilities.

Suffering may also occur as an unavoidable by-product of normal and vital functions—such as human childbirth, which is painful and risky to a degree unique among mammals. This came about in human evolution because of conflicting selective pressures for efficient bipedal locomotion in adults (which calls for a narrow pelvis) and for a larger brain in their offspring (which requires a wider pelvis for the child's head to pass through). The anatomy of human females today represents an evolutionary compromise that is uncomfortable, to put it mildly. But the payoffs are hands free for toolmaking, and a human brain to guide them. Suffering, then, may have been inseparable from both our physical and our social evolution—which is to say, from the origins of our very humanity.

Death. And as for death: life could not spread and evolve on a finite planet if death did not recycle space, energy, and materials, and cull undesirable genes from populations. Death may even be of adaptive value to those that die. After giving its offspring a start in life, an individual may sometimes best help them by dying and getting out of their way. If the individual belongs to a tightly-knit collective of close kin (like an ant colony), kin selection may lead it to sacrifice its own reproduction, or even its life, to benefit its siblings and their offspring. In the extreme case, this collective is a multicellular organism like each of us—made up of genetically identical cells each liable to death, a death distinct from (yet connected to) that of the organism as a whole (see Clark 1996 for an excellent discussion).

As single cells evolved to form multicellular organisms, normal growth and function required that some cells self-destruct according to precise, genetically-programmed timetables. Hence, a tadpole's tail is deleted as it transforms into a frog, and the cells lining a woman's uterus die and are shed on a monthly schedule. Flowers fade quickly once pollinated so the plant's energy can be channeled into producing fruit and seeds. (This programmed suicide of cells is called apoptosis—literally "dropping off," as with flower petals or autumn leaves.) Cell death even creates important body parts that are permanent or constantly renewed, such as the corneas and lenses of our eyes and our outermost layer of skin. Cells of the immune system that destroy invading microbes or the body's own mutated, possibly cancerous cells (often by inducing them to self-destruct) also destroy themselves if they fail to find a suitable target.

Another big reason why cells self-destruct is because they have suffered damage, especially to their DNA, that exceeds their capacity for self-repair. Because such damage tends to accumulate over time as the DNA is copied and recopied during cell division and metabolism, programmed cell death turns out to be intimately involved in senescence, or aging.

Surprisingly, aging is not always, and has not always been, an inevitable part of life. The earliest single-celled organisms, like modern bacteria, reproduced by asexual cell division. Such an organism—a single cell—never truly dies as long as it keeps dividing; barring accidental death, it is in effect immortal. Programmed death evolved at about the same time as sexual reproduction, back when our ancestors were still single-celled, perhaps a billion years after the origin of life.

Sex speeded up evolution by increasing genetic variety. Together with multicellularity, it made possible the large, complex, versatile kinds of creatures that we ourselves are and that we see around us today. But one cost of this complexity was increased wear and tear on the DNA "instruction manuals" in each of the body's cells during a lengthier growth and life span. Constant "reading" of these "manuals" by the machinery in the body's cells, plus other sources of cumulative damage, eventually degrades the DNA molecules till they are not fit to be copied for the next generation. Thus it became necessary to sequester pristine copies of each individual's DNA (for example, in the germ cells), to be consulted only at the time of reproduction and not for "everyday use."

The DNA in the "somatic" cells making up the rest of the body then became, in a sense, expendable. These somatic copies of the DNA are not only at greater risk of damage, but are reproductively irrelevant; they are never passed on to offspring. From the viewpoint of the "selfish genes," the bodies these somatic copies construct serve only to pass on the DNA in the germ cells: in the biologist's cliché, a chicken is just an egg's way of making more eggs. When the somatic cells are too far gone to use or repair (hopefully, after reproduction has occurred), they simply die. Unfortunately, these somatic cells are us: our bodies, including especially our brains. Inevitable aging and death are a price we pay for having evolved to a certain level of bodily complexity.

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